This invention pertains to instruments in the mechanical and technical drafting field used for drawing straight lines and specifically to an electronic drafting instrument which measures and displays its own linear displacement.
Despite the sophistication of modern engineering graphics, the measuring tools and techniques used by most draftsmen are essentially the same today as they were a century ago.
Most drafting measurements are made with scales, and dividers. When a scale is used to layout a measurement, an index mark on the scale is placed opposite a reference mark on the drawing another mark is placed opposite the desired measurement on the scale. An assortment of scales is usually required to accommodate different measuring units and scale factors.
When greater accuracy is required, measurements are usually taken between the open points of a pair of dividers and transferred to the drawing media by lightly pinpricking their location.
Using scales for layout measurements on complex drawings is time consuming, tedious and often eyestraining even for those with special skills.
It is, therefore, an object of this invention to provide a drafting instrument that will increase drawing efficiency, and reduce tedium and eyestrain.
The concept used to achieve that objective is embodied in an integral straightedged electronic drafting instrument which measures its own displacement and digitally displays the numbers in a large fixed size which is easy to read without eyestrain or the need for optical magnifiers.
The concept of a straightedge with some form of direct readout is old, but the physical embodiment of that concept taught in prior art such as U.S. Pat. Nos. 287,200 of Wach; 1,051,712 of Eager; 2,064,142 of Barany and 3,726,017 of DeMathe all have limitations for the professional draftsman.
Two of these limitations are: 1. lack of convenient easily read mean for displaying the total displacement beyond one revolution of a mechanical dial, 2. lack of convenient efficient means for automatically resetting the readout to zero.
In contrast to mechanical prior art self-measuring drafting instruments, this invention utilizes an electronic displacement sensor, an electronic up-down counter combined with a calculator type circuit, and an electronic digital display to overcome all of the above deficienceis.
The electronic principles involved are well known and are used, for example, in digital readout systems for lathes and milling machines, electronic digital planimeters, and electronic linear measuring probes.
Electronic linear measuring probes, which are electronic versions of mechanical cartometers, are of special interest because they could indeed by used to measure distances on drawings, as well as on maps. However, these probes are too cumbersome for creating original drawings because the readout, connected via a cable to the pen-like probe, is remote from the measuring probe. This is a serious limitation because the user is required to look away from the drawing surface to read the measurement corresponding to each probe position. Still another limitation is that such probes must be used in conjunction with a separate straightedge, and to draw a line the full length of the straightedge, the probe must be removed to make way for a pen or pencil.
It is, therefore, another object of this invention to provide an integral straightedged electronic drafting instrument which electronically measures its own displacement and gives a continuous readout of the linear displacement directly on the straightedge so the user does not have to look away from the drawing surface to read the digital display.
Yet another object of this invention is to provide an integral straightedged electronic drafting instrument which measures and displays its own displacement and can be used as a direct replacement for conventional scales and straightedges used on state-of-the-art drafting machines.
Another limitation of the prior art is that no means is provided to warn the user if the instrument is unknowingly lifted from the drawing surface during a measurement. This is important because the displayed results would be less than the true displacement. It is, therefore, another object of this invention to provide an integral straightedged drafting instrument which measures and displays its own displacement and has a contact sensor and annunciator to warn the user whenever the instrument is lifted such that the measurement may be in error.